Re: [PATCH] kernel/rcutorture.c: use scnprintf() instead of sprintf()

[Chen Gang <gang.chen@asianux.com>]

On 10/14/2013 07:28 PM, Paul E. McKenney wrote:
> On Mon, Oct 14, 2013 at 04:38:55PM +0800, Chen Gang wrote:
>> If the contents is more than 4096 bytes (e.g. if have 1K cpus), current
>> sprintf() will cause memory overflow.
>>
>> They are all test information which can be truncated, so use scnprintf()
>> instead of sprintf(), also add 'max' parameter for related functions,
>> also notice 80 columns boundary and parameters alignments.
>>
>> Test case:
>>
>>   Fedora16 x86_64, 2 CPUs, 2GB RAM, [in/rm]mod with "torture_type=srcu".
>>
>>     let maximize buffer to 256 to truncate in rcu_torture_printk().
>>     let maximize buffer to 410 to may truncate in srcu_torture_stats().
>>     let maximize buffer to 4096 (original size) to print full.
>>
>>   it is a rcu test module, so not need additional test or consideration.
>>
>> Signed-off-by: Chen Gang <gang.chen@asianux.com>
> 
> At first glance, not a bad start.
> 
> Suppose that your goal was to make it avoid truncation.  What would you
> do differently?
> 

One simple way: using snprintf() instead of scnprintf() in the related
printing functions. Then call them with "buffer == NULL" to get buffer
size, next allocate it and call it again ...

Hmm... it is only a test module, is it worth enough to try to make it
avoid truncation? If some members (quite few members) find truncation,
they can simply extend maximize buffer to avoid it when testing.

But if we do not fix this bug, when memory overflow, the OS may not stop
immediately, then it will/may lead the testers to face various amazing
things (which is not quite easy to find root cause).


All together, making contribution with efficiency and without negative
effect is our goal, so ...


Thanks.

> 							Thanx, Paul
> 
>> ---
>>  kernel/rcutorture.c |  110 +++++++++++++++++++++++++++-----------------------
>>  1 files changed, 59 insertions(+), 51 deletions(-)
>>
>> diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
>> index be63101..107fd76 100644
>> --- a/kernel/rcutorture.c
>> +++ b/kernel/rcutorture.c
>> @@ -370,7 +370,7 @@ struct rcu_torture_ops {
>>  	void (*call)(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
>>  	void (*cb_barrier)(void);
>>  	void (*fqs)(void);
>> -	int (*stats)(char *page);
>> +	int (*stats)(char *page, int max);
>>  	int irq_capable;
>>  	int can_boost;
>>  	const char *name;
>> @@ -572,20 +572,20 @@ static void srcu_torture_barrier(void)
>>  	srcu_barrier(&srcu_ctl);
>>  }
>>
>> -static int srcu_torture_stats(char *page)
>> +static int srcu_torture_stats(char *page, int max)
>>  {
>>  	int cnt = 0;
>>  	int cpu;
>>  	int idx = srcu_ctl.completed & 0x1;
>>
>> -	cnt += sprintf(&page[cnt], "%s%s per-CPU(idx=%d):",
>> -		       torture_type, TORTURE_FLAG, idx);
>> +	cnt += scnprintf(&page[cnt], max - cnt, "%s%s per-CPU(idx=%d):",
>> +			torture_type, TORTURE_FLAG, idx);
>>  	for_each_possible_cpu(cpu) {
>> -		cnt += sprintf(&page[cnt], " %d(%lu,%lu)", cpu,
>> -			       per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[!idx],
>> -			       per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[idx]);
>> +		cnt += scnprintf(&page[cnt], max - cnt, " %d(%lu,%lu)", cpu,
>> +				per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[!idx],
>> +				per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[idx]);
>>  	}
>> -	cnt += sprintf(&page[cnt], "\n");
>> +	cnt += scnprintf(&page[cnt], max - cnt, "\n");
>>  	return cnt;
>>  }
>>
>> @@ -1047,7 +1047,7 @@ rcu_torture_reader(void *arg)
>>   * Create an RCU-torture statistics message in the specified buffer.
>>   */
>>  static int
>> -rcu_torture_printk(char *page)
>> +rcu_torture_printk(char *page, int max)
>>  {
>>  	int cnt = 0;
>>  	int cpu;
>> @@ -1065,61 +1065,69 @@ rcu_torture_printk(char *page)
>>  		if (pipesummary[i] != 0)
>>  			break;
>>  	}
>> -	cnt += sprintf(&page[cnt], "%s%s ", torture_type, TORTURE_FLAG);
>> -	cnt += sprintf(&page[cnt],
>> -		       "rtc: %p ver: %lu tfle: %d rta: %d rtaf: %d rtf: %d ",
>> -		       rcu_torture_current,
>> -		       rcu_torture_current_version,
>> -		       list_empty(&rcu_torture_freelist),
>> -		       atomic_read(&n_rcu_torture_alloc),
>> -		       atomic_read(&n_rcu_torture_alloc_fail),
>> -		       atomic_read(&n_rcu_torture_free));
>> -	cnt += sprintf(&page[cnt], "rtmbe: %d rtbke: %ld rtbre: %ld ",
>> -		       atomic_read(&n_rcu_torture_mberror),
>> -		       n_rcu_torture_boost_ktrerror,
>> -		       n_rcu_torture_boost_rterror);
>> -	cnt += sprintf(&page[cnt], "rtbf: %ld rtb: %ld nt: %ld ",
>> -		       n_rcu_torture_boost_failure,
>> -		       n_rcu_torture_boosts,
>> -		       n_rcu_torture_timers);
>> -	cnt += sprintf(&page[cnt],
>> -		       "onoff: %ld/%ld:%ld/%ld %d,%d:%d,%d %lu:%lu (HZ=%d) ",
>> -		       n_online_successes, n_online_attempts,
>> -		       n_offline_successes, n_offline_attempts,
>> -		       min_online, max_online,
>> -		       min_offline, max_offline,
>> -		       sum_online, sum_offline, HZ);
>> -	cnt += sprintf(&page[cnt], "barrier: %ld/%ld:%ld",
>> -		       n_barrier_successes,
>> -		       n_barrier_attempts,
>> -		       n_rcu_torture_barrier_error);
>> -	cnt += sprintf(&page[cnt], "\n%s%s ", torture_type, TORTURE_FLAG);
>> +	cnt += scnprintf(&page[cnt], max - cnt, "%s%s ",
>> +			torture_type, TORTURE_FLAG);
>> +	cnt += scnprintf(&page[cnt], max - cnt,
>> +			"rtc: %p ver: %lu tfle: %d rta: %d rtaf: %d rtf: %d ",
>> +			rcu_torture_current,
>> +			rcu_torture_current_version,
>> +			list_empty(&rcu_torture_freelist),
>> +			atomic_read(&n_rcu_torture_alloc),
>> +			atomic_read(&n_rcu_torture_alloc_fail),
>> +			atomic_read(&n_rcu_torture_free));
>> +	cnt += scnprintf(&page[cnt], max - cnt,
>> +			"rtmbe: %d rtbke: %ld rtbre: %ld ",
>> +			atomic_read(&n_rcu_torture_mberror),
>> +			n_rcu_torture_boost_ktrerror,
>> +			n_rcu_torture_boost_rterror);
>> +	cnt += scnprintf(&page[cnt], max - cnt,
>> +			"rtbf: %ld rtb: %ld nt: %ld ",
>> +			n_rcu_torture_boost_failure,
>> +			n_rcu_torture_boosts,
>> +			n_rcu_torture_timers);
>> +	cnt += scnprintf(&page[cnt], max - cnt,
>> +			"onoff: %ld/%ld:%ld/%ld %d,%d:%d,%d %lu:%lu (HZ=%d) ",
>> +			n_online_successes, n_online_attempts,
>> +			n_offline_successes, n_offline_attempts,
>> +			min_online, max_online,
>> +			min_offline, max_offline,
>> +			sum_online, sum_offline, HZ);
>> +	cnt += scnprintf(&page[cnt], max - cnt,
>> +			"barrier: %ld/%ld:%ld",
>> +			n_barrier_successes,
>> +			n_barrier_attempts,
>> +			n_rcu_torture_barrier_error);
>> +	cnt += scnprintf(&page[cnt], max - cnt, "\n%s%s ",
>> +			torture_type, TORTURE_FLAG);
>>  	if (atomic_read(&n_rcu_torture_mberror) != 0 ||
>>  	    n_rcu_torture_barrier_error != 0 ||
>>  	    n_rcu_torture_boost_ktrerror != 0 ||
>>  	    n_rcu_torture_boost_rterror != 0 ||
>>  	    n_rcu_torture_boost_failure != 0 ||
>>  	    i > 1) {
>> -		cnt += sprintf(&page[cnt], "!!! ");
>> +		cnt += scnprintf(&page[cnt], max - cnt, "!!! ");
>>  		atomic_inc(&n_rcu_torture_error);
>>  		WARN_ON_ONCE(1);
>>  	}
>> -	cnt += sprintf(&page[cnt], "Reader Pipe: ");
>> +	cnt += scnprintf(&page[cnt], max - cnt, "Reader Pipe: ");
>>  	for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
>> -		cnt += sprintf(&page[cnt], " %ld", pipesummary[i]);
>> -	cnt += sprintf(&page[cnt], "\n%s%s ", torture_type, TORTURE_FLAG);
>> -	cnt += sprintf(&page[cnt], "Reader Batch: ");
>> +		cnt += scnprintf(&page[cnt], max - cnt, " %ld", pipesummary[i]);
>> +	cnt += scnprintf(&page[cnt], max - cnt, "\n%s%s ",
>> +			torture_type, TORTURE_FLAG);
>> +	cnt += scnprintf(&page[cnt], max - cnt, "Reader Batch: ");
>>  	for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
>> -		cnt += sprintf(&page[cnt], " %ld", batchsummary[i]);
>> -	cnt += sprintf(&page[cnt], "\n%s%s ", torture_type, TORTURE_FLAG);
>> -	cnt += sprintf(&page[cnt], "Free-Block Circulation: ");
>> +		cnt += scnprintf(&page[cnt], max - cnt, " %ld",
>> +				batchsummary[i]);
>> +	cnt += scnprintf(&page[cnt], max - cnt, "\n%s%s ",
>> +			torture_type, TORTURE_FLAG);
>> +	cnt += scnprintf(&page[cnt], max - cnt, "Free-Block Circulation: ");
>>  	for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
>> -		cnt += sprintf(&page[cnt], " %d",
>> -			       atomic_read(&rcu_torture_wcount[i]));
>> +		cnt += scnprintf(&page[cnt], max - cnt, " %d",
>> +				atomic_read(&rcu_torture_wcount[i]));
>>  	}
>> -	cnt += sprintf(&page[cnt], "\n");
>> +	cnt += scnprintf(&page[cnt], max - cnt, "\n");
>>  	if (cur_ops->stats)
>> -		cnt += cur_ops->stats(&page[cnt]);
>> +		cnt += cur_ops->stats(&page[cnt], max - cnt);
>>  	return cnt;
>>  }
>>
>> @@ -1136,7 +1144,7 @@ rcu_torture_stats_print(void)
>>  {
>>  	int cnt;
>>
>> -	cnt = rcu_torture_printk(printk_buf);
>> +	cnt = rcu_torture_printk(printk_buf, sizeof(printk_buf));
>>  	pr_alert("%s", printk_buf);
>>  }
>>
>> -- 
>> 1.7.7.6
>>
> 
> 
> 


-- 
Chen Gang